The current invention concerns corrosion inhibitors useful in heat transfer fluids. More particularly, this invention concerns metal corrosion inhibition in heat transfer fluids such as coolants useful in automobile engines.
Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron, aluminum andd their alloys. The possibility of corrosive attack on these metals in automobile engines is high due to the presence of various ions as well as the high tempertures, pressures and flowrates found in the cooling systems of modern engines. The presence of corrosion products in the cooling system can and does interfere with the heat transfer from the combustion chambers which subsequently may cause overheating and engine component failure due to the excessive metal temperatures.
It would thus be desirable to prevent or substantially decrease the formation of corrosion products within engine cooling systems. One well-recognized method for accomplishing this goal is the addition of corrosion inhibitors to the coolants typically used in automotive engines. Various inhibitors have been identified as useful for this purpose. Examples of such inhibitors include silicates, amines, nitrates, borates, molybdates, and triazoles either alone or in various combinations. For a discussion of the state of the art, see, e.g., U.S. Pat. No. 4,647,392 hereby incorporated by reference which discusses various inhibitor compositions.
Various problems exist with known inhibitors. These problems include toxicity and environmental concerns, the use of expensive materials and the degradation of the inhibitor composition under actual use conditions. Further, many existing inhibitor compositions have only limited effect in protecting lighter metals such as aluminum currently finding use in automotive engines. Thus, what is needed are coolant compositions which are environmentally acceptable, use readily available and relatively inexpensive materials and are more effective in protecting aluminum engine parts than traditional corrosion inhibitors.